Open-structure dam



Nov. 26, 1929. E. PROBST ET AL OPEN STRUCTURE DAM 2 Sheets-Sheet 1 Filed Nov. 10, 1928 IN VEN TORS Q WMC 1m A TTORNE Y.

Nov. 26, 1929. E. PRoBsT ET AL v 1,736,939

' OPEN STRUCTURE DAM 2 Sheets-Sheet 2 Filed Nov. 10, 1928 IN VEN TORJ fit av. ATTORNEY PBOBST AND FRIEDEICH T'GLIZ LE, 0151 KARLSRUHE, GERMANY OPEN-STRUCTURE DAM Application filed November 10, 1928, Serial No. 318,521, and in Germany July 17, 1828.

Our invention relates to open-structure dams and is herein described with particular consideration of economically and hydromecha-nically advantageous forms of application to various heights of damining, to wit, low dams w'tl'i a maximal head up to 60 feet, medium dams with a maximal head from 60 to 100 feet and high dams with a maximal head of more than 100 feet.

In the drawings in which Figs. 1 and 2 illustrate the inventive idea in its broadest aspect, which is particularly advantageous for dams about 160 feet high, while 3 shows the adaptation of our invention to a dam of mean height, Fig. 1 is a plan view of a section 01" a dam, Fig. 2 vertical section at right angles to the dam and Fig. 3 a perspective view ot a dam from the head water side.

Similar numerals refer to similar parts 29 throughout the various views:

(4) According to Figs. 1 and 2, a series of vertical, substantially triangular supporting partitions 1, 2, extending at right angles to the dam are founded a adequate depth on solid rock. The sides of the partitions 1 in the longitudinal direction bear the numerals 3 and 4 and those of the partitions 2 the numerals 5 and 6. Between the sides 41 and 5 are provided upright circular arches 7 whose intrados 8 includes an angle of 180 at the center and merges tangentially into the sides 1- and 5 of the supporting partitions, whereas the extrados 9 is extended to the intersection with the sides i and 5. The arches stop short at the base at a distance of about 3 to 6 feet,

forming at the same time a support for a horizontal slab 10 extending between the sides d and 5. supported along its entire extent and resting on the head water side on an invert 11 deeply built into the solid rock and likewise extending between the sides 1 and 5. Between the sides 8 and 6 extends a slab 12, the head water elevation 13 of which is vertical, lying in the plane formed by the connection of the lines in which the intrados 8 merges into the sides a and 5 of the partitions.

The tail water elevation 14- may be inclined as shown, or formed in steps. The slab 12 stops at the same distance above the base as the arches forming at the same time a support for a horizontal plate 15 extending between the sides 3 and 6 and also supported along its entire extent. The slab 15 rests on the head water side on an invert 16 built deeply into the solid rock. For bracing the portions of the partitions 1 and 2 on the tail water side, vertical ribs 1'? extending between the sides 3 and 6 are provided, which are built into the solid rock as spurs 18, also ledges being provided for that purpose. Spurs, 20, are provided constituting the tail water discharge.

(2)) For mean heightdams 3) it can always be arranged that the head water dam walls of the horizontal slabs 10 and 15 are in straight line enabling a single, continuous, deeply built invert 11, 16 which is highly desirable from a hydromechanical point of view. In this case it will be advisable to dispense completely with the portions of the partitions 1, 2 which extend on the outside of the arches toward the head water side. The thus produced horizontal slab 10, 15 extending in longitudinal direction is suspended on the tail water side from the head water dam wall, being supported on the head water side on the continuous invert 11, 16.

(a) It may be advantageous to entirely dispense with the horizontal slabs 10 and the cor responding inverts 11 and instead to build the upright arches 7 to a considerable depth into solid rock, it the strength of the arches permits it, as is possible in the case of high dams or large diameters of the arches.

(d) Vice versa, in low dams, the horizontalslabs 15 and the corresponding inverts 16 may be dispensed with, and instead the slabs 12 are built deeply into the solid rock as inverts.

(e) In the case of low dams and small spans, it may be advisable to replace the vertical arches 7 by vertical. slabs on the order of the slabs 12, which under certain conditions can be in one line with said slabs 12. In this very simple and economical construction, the result is a common invert 11, 16 and generally also an equal spacing of the partitions 1, 2. i

(f) Also for low dams, yet another modification should be mentioned in which the plates 12 and 15 as well as the inverts 16 are omitted, and always two partitions 1 and 2 are combined into one support. In that case, the tail water side portion of the partitions is reinforced by braces in the manner of the ledges 19.

(9) Of course, the classification of the modifications enumerated in the above paragraphs according to low, mean and higii dams does not preclude all the dams from being built for any height.

Experience had with dams of the "ravity as well as of the open-structure types has, as regards their stability, not been of sumcient help to enable the construction being carried out on uniform basis of design. This is shown by the great variety of an planations and interpretations which, for instance, are given for the calculation of gravity-type dams and their static proof. lily invention has its origin in the endeavr to produce a construction wnich on the basis of a statically sound solution enables the builder to produce a safe stability, at the same time offering economical advantages as compared with the gravity-type dams and advantages of construction over the old openstructure dams. The following paragraphs will prove the correctness of the foregoing statements.

1. Stability conditions There have been heretofore essentially two types of open-structure dams which principally show very little difference. Both these types create through an incline of the damwall on the head Water sidein addi tion to the horizontal,a perpendicular component of the water pressure whereby the stability of the structure is insured. In most dams, the angle of the dam wall on the head water side relative to the perpendicular is a little below 45 degrees. To increase the stability would mean an enlargement of this angle involving a considerable increase in the cost of he whole structure.

One of the above mentioned types makes use of slabs arranged at an incline which abut against the real supports at distances of about fifte .1 feet, whereas the other type utilizes the arch effect of aseries of obliquely arranged arches to enable the supports to be spaced wider apart. In both types angular supports located behind the head water dam wall transmit the inclined water pressure of the dam wall on therhead water side to the solid rock. In many cases, all the structural parts are deeply cut into the solid rock to increase the surety against a horizontal sliding of the dam, since the horizontal componentof the water pressure in most instances is not much below the sum of all perpendicular forces. 7

As compared therewith, the present invention permits the attainment of any desired degree of stability without a considerable increase in cost. The above described constructions provide a vertical head water dam wall in connection with a horizontal plate which is located from 3 to 6 feet above the to overcomethe lifting tendency, which plate may be called the counterweight-carrier. The characteristic feature of this in= vention is therefore a complete separation of the counterweight-carrier from the plane receiving the horizontal water pressure. An increase in the stability is thus made possible by the simplest means through a correspond ing extension of the horizontal surface.

In addition, the counter-weight of the resting water column acts in this invention vith almost twice the intensity of the old methods of construction.

If the dam wall is inclined, the vertical component of the Water pressure is zero at the top and reaches the maximum hydrostatic pressure only at the bottom of the incline; at the center the counterweight water column is only half the full water head. In 1 practice, this fact, under equal conditions of stability means a considerably shorter base length of the supporting partitions or with an equal base length of the partitions a very much desired increase in the stability of structure as compared with the old constructions.

l Vith a clear understanding of the component forces one can obtain any degree of stability and as regards the same, surpass evenv the gravity-type dams.

A comparison of the cross-sections and the stresses as regards the various structural members is in favor of the above described constructions, particularly from the hydromechanically very important viewpoint of avoiding the formation of cracks in the cross sections exposed to the water. The heretofore mostly practised single-wall support does not, where obliquely disposed arches are used, permit an essential increase of the maximum center angle of the arcuate surface exposed to the water above 135. .Vith such an angle, even with a uniformly dist l uted water-pressure at the skew-back, on the trades, the stress is zero, while on the trados the stress is twice that of a closed annular body subjected everywhere to a uniform pressure. The additional component of the weight of the arch and of the nly L LllG distributed water pressure creates con iuerable stress on the extrados eXposedto the wa andalarge pressure on the intrados. Thus,particularly on the surface exposed to the water, there is ever the danger of the formation of tensional cracks, which may be reduced by,

Compared therewith, this invention permits the construction of 180 arches through the connection of the slabs 12 with the arches in alternate succession, in which arch construction, if there is a uniform distribution of the radial loads, the stresses differ only very slightly from those of a closed body subj ected everywhere to uniform pressures.

In addition, because of the vertical position of the arches, their own weight and unevenly distributed water pressure do not need to be considered so that the stresses on the extrados are not essentially smaller than those on the intrados.

It is also known, that in a 135 arch the stresses due to temperature are, under equal circumstances, twice those of a 180 arch, which is also an important view point.

Of course, all the slabs (12, 10, 15) are reinforced. The vertical slabs 12 weigh about the same as an inclined arch; the larger unit weight is balanced by the fact that the arcs are 1.3 times the length of the corresponding base. A great advantage of the serial arrangement of slabs and arches is that the joining of the slabs 12 at the arcs 7 is practically very small, so that the side of the slab exposed to the water is rather free from any considerable tensile stresses.

The slabs 15 in the construction under behave essentially as slightly elastic fixed beams on two supports. Since for practical reasons, the slabs are otherwise made of the same thickness, it is easy to prevent the occurrence of cracks at the points of support. The same applies to In the construction sub (6) in which the advantage of a common continuous invert was obtained, considerable negative moments in the slabs 10 and can be avoided if the head water portions of the supports are omitted as described under Since for practical reasons, the cross-section is made of uniform thickness, the formation of tensional cracks on the water side is eliminated.

In the constructions sub a, h, d, the support of the slabs 10, 15 can be so selected that the danger of cracks in the arches 7, due to longitudinal tension, only is present at the 'atrados exposed to the water.

The supporting partitions, especially toward the head water side, maybe referred to as comparatively strongly reinforced structural parts provided that the head water parts are not dispensed with. The saving in materials as compared with the old constructions is very considerable, not so mucl in the supporting partitions themselves, but rather due to the elimination of complicated angular reinforcement-s. The head water side portions of the supporting partitions are, as far as th y are used, essentially drawn, since they only serve as suspension members for the counterweightslabs; thus, about half the supporting surface needs no reinforcements.

It should be noted that this drawn half is on both sides under water and therefore has nothing to do with the water tightness of the dam. The part of the dam, which is under pressure, has already a very strong reinforcement in the vertical plates 12 which is ample for low dams, with water heads up to :5 feet including the spur 20. Up to a 120 feet water head, the insertion of a vertical rib 17 is advisable, whereas beyond that height the construction shown in Fig. 2 is selected. It should not be overlooked that the vertical ribs 17 and also the spur must also act as carriers thus decreasing the bottom pressure, whereas, the spurs 18 and 20 constitute a further increase in the safety against horizontal sliding.

Summing up it may be stated that this invention permits the construction of openstructure dams of any desired stability, so that all danger of tensional cracks on the head water side of the structural members is eliminated. In addition, with a proper select-ion of the constructions outlined under a-g, a very economical saving in materials, as compared with the old constructions may be attained.

II. Simplified construction The economical and technical principal advantage of the constructions described. under ag lies in the simplicity of the erection of the dam, particularly when compared with the inclined arches. The construction of the latter is very expensive, firstly on account of the moulds required, where the bi-lateral arch effect must be considered; secondly, on account of the low working height determined by the inclined disposition of the moulds, whereby the pouring of the concrete is seriously impeded and made more expensive.

On the other hand, the vertical arches do not cause any more trouble in respects to moulds and the pouring than the partitions; moreover, the thickness of the arches may be maintained constant throughout, without ad dition of material, for dams up to 100 feet high, because of their verticaldisposition. The same applies to the vertical slabs 12 and to the polygonal arrangement according to the construction sub (g).

Especially simple is the manufacture of the lower horizontal slabs 10 and 15 located at a height of 3 to 6 feet above the solid rock, since they must be constructed of'uniform thickness.

HI. Simplified foundation It is well known that the safety of dams is increased by the depth at which the inverts out into the solid rock. In the old constructions having inclined arches this is accom plished by continuing the arches into the rock, the portion extending into the rock be ing vertically disposed. To obtain a good joint, the arches are made very considerably heavier for a length about twice that of the depth of the joint and frequently more than twice.

Instead of that, this invention provides,- for instance the construction sub (2')) which is preferably considered for the most frequent heights of damming,-a continuous, straight invert. As appears from 2, said invert is so constructed as to be able to withstand considerable horizontal forces, the transmission of those forces to the invert being affected by the horizontal slabs 10 and 15 which invert, as compared to the length 3) is very deep, offering an absolute guarantee for a uniform share of the entire invert in preventing the danger of a horizontal slide. To obtain the same amount of safety for inclined arches, they require the above mentioned addition of considerable material which is not required in the new construction, since the slabs 10 and 15 fulfill the requirements.

The horizontal cross-sections of inclined arches are lengthened ellipses. The invert in this well-known construction is therefore composed of a series of such curves. Compared therewith, according to this invention, the invert, except in the construction sub (0) is straight-lined, and its length is shorted by about 35% than the old construction, while its effect is the same. That means a considerable saving in excavation and founda tion expenses, particularly since in many instances, especially in open-structure dams, the rock is very hard.

Finally, in the vertical arrangement of the head water side top surface, attention should be called to the free disposition of the de signer as regards the division of the width of the dam. That the width of the slabs 12 is chosen considerably smaller than the diameter of the arches is self-understood. Mention has already been made, that in the case of inclined slabs it is not advisable to exceed a distance of 15 feet between supports; in the case of inclined arches this limit should be about 40 feet, since otherwise the framework required for the inclined arches would be too expensive and too heavy. Since there is hardly any difference, as has already been mentioned, in the cost whether a vertical arch is made in concrete or as a support, an increase of the diameter of the arches is only limited by the necessary addition of material for the arches. Therefore, one will have to examine, to what extent the simplification of construction economically warrant-s such an addition of materials. In any event, this invention ofiers an entirely different range of possibilities in this respect. There may be, for instance, a good rock generally suitable for the foundation, but showir a bad fault in the direction of the valley to the extent of about feet which one does not care to place under a load without taking a permanent risk.

In a very simple manner, the new construction would provide for an arch of a diameter of 100 feet so that the supports would be, for a distance of 15 feet, on solid roclr. According to the construction sub (0), vertical arches with deeply out inverts would be chosen.

This one example illustrates that this invention not only economical and hydromechanical advantages and improvements can be obtained, but it also offers means to overcome dl'lllCUlillQS which heretofore could not be mastered.

V] e claim:

1. In a dam, the combination of a head water dam wall, a substantially horizontal counterweight carrier joined to the lower edge of said dam wall and extending upstream therefrom, and an invert connecting said counterweight carrier with the stream bed at a point spaced upstream with respect to said dam wall, said counterweight carrier being disposed above the stream bed to provide an space therebeneath.

2. In a dam, the combination of a head water dam wall inclusive of arches and intermediate straight portions, a substantially horizontal counterweight carrier joined to the lower edge of said dam wall and extending upstream therefrom, tension ribs con necting said counterweight carrier with said dam wall at the points of junction of the arched and straight portions of the latter, and an invert connecting said counterweight carrier wlth the stream bed at a point spaced upstream from said damwall, said counterweight carrier being disposed above the stream bed to provide an air space therebeneath.

3. In dam, the combination of a head water dam wall, a substantially horizontal counterweight carrier joined to the lower edge of said dam wall and extending upstream therefrom, and means to prevent headwater seepage pressure from acting upwardly against the bottom of said counterweight carrier. i

In testimony whereof we affix our signatures.

nnrn raonsr. rninnnron Torus. 

